Magnetic field regenerator

ABSTRACT

An example particle accelerator includes the following: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a plasma column, where the cavity has a magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity; an extraction channel to receive the particles accelerated from the plasma column and to output the received particles from the cavity; and a regenerator to provide a magnetic field bump within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, particles output to the extraction channel. The magnetic field is at least 6 Tesla and the magnetic field bump is at most 2 Tesla.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/039,652, which was filed on Sep. 27, 2013 and which issued as U.S.Pat. No. 9,622,334 on Apr. 11, 2017. Priority is hereby claimed to U.S.patent application Ser. No. 14/039,652. The contents of U.S. patentapplication Ser. No. 14/039,652 are incorporated by reference into thisdisclosure. Priority is hereby also claimed to U.S. ProvisionalApplication No. 61/707,590, which was filed on Sep. 28, 2012. Thecontents of U.S. Provisional Application No. 61/707,590 are herebyincorporated by reference into this disclosure.

TECHNICAL FIELD

This disclosure relates generally to a magnetic field regenerator foruse in a particle accelerator.

BACKGROUND

Particle therapy systems use an accelerator to generate a particle beamfor treating afflictions, such as tumors. In operation, particles areaccelerated in orbits inside a cavity in the presence of a magneticfield, and removed from the cavity through an extraction channel. Amagnetic field regenerator generates a magnetic field bump near theoutside of the cavity to distort the pitch and angle of some orbits sothat they precess towards, and eventually into, the extraction channel.A magnetic field regenerator is typically a ferromagnetic arrangementthat provides an enhancement to an existing magnetic field.

Heretofore, particle accelerators operated using a relatively lowmagnetic field, e.g., on the order of 2 Tesla. In such cases, themagnetic field bump produced by the magnetic field regenerator could“suck” a significant amount of the magnetic flux from the interiormagnetic fields. This creates a magnetic field hole in the cavityrelative to the background 2 Tesla magnetic field. This hole wastypically filled by incorporating progressively smallerradially-adjacent magnetic field regenerators into the cavity to addprogressively smaller magnetic field bumps in place of correspondingholes generated each by an immediately preceding magnetic fieldregenerator. Implementing the foregoing magnetic field correction usingprogressively smaller magnetic field regenerators can be difficult insystems that operate at relatively low magnetic fields.

SUMMARY

An example particle accelerator includes the following: a voltage sourceto provide a radio frequency (RF) voltage to a cavity to accelerateparticles from a plasma column, where the cavity has a magnetic fieldcausing particles accelerated from the plasma column to move orbitallywithin the cavity; an extraction channel to receive the particlesaccelerated from the plasma column and to output the received particlesfrom the cavity; and a regenerator to provide a magnetic field bumpwithin the cavity to thereby change successive orbits of the particlesaccelerated from the plasma column so that, eventually, particles outputto the extraction channel. The magnetic field is at least 4 Tesla or 6Tesla and the magnetic field bump is at most 2 Tesla. The exampleparticle accelerator may include one or more of the following features,either alone or in combination.

The regenerator may include a ferromagnetic arrangement located at aradial location from the plasma column. The regenerator may include asingle ferromagnetic arrangement or multiple ferromagnetic arrangements(e.g., there may be multiple ferromagnetic structures of the typedescribed herein configured and arranged to produce the magnetic fieldbump and/or to shape the magnetic field bump). The ferromagneticstructure may include steel. The magnetic field may be at least 4 Teslaor 8 Tesla and the magnetic field bump may be at most 2 Tesla.

The regenerator may have an irregular cross-sectional shape that isdesigned to produce a magnetic field bump having a specific shape and/ormagnitude. The cross-sectional irregular shape may have an angularfeature on a portion of the regenerator facing towards the cavity, wherethe angular feature includes an edge comprising a non-orthogonalintersection of two faces.

The extraction channel may include a septum that separates particlesentering the extraction channel from particles remaining in the cavity.The regenerator may be configured so that a pitch and an angle of aparticle orbit enable a majority of particles in the particle orbit topass over the septum and into the extraction channel. The particle orbitpassing over the septum may include a range of radii of particlesrelative to the plasma column.

An example proton therapy system includes the foregoing particleaccelerator; and a gantry on which the synchrocyclotron is mounted. Thegantry is rotatable relative to a patient position. Protons are outputessentially directly from the synchrocyclotron to the patient position.The particle accelerator may be a synchrocyclotron.

An example particle accelerator includes the following: a particlesource to provide pulses of ionized plasma to a cavity containing amagnetic field; a voltage source to provide a radio frequency (RF)voltage to the cavity to accelerate particles from the plasma columnoutwardly, where the particles accelerated from the plasma column travelin orbits within the cavity; an extraction channel to receive orbits ofparticles from the cavity for output from the particle accelerator and aregenerator to provide a magnetic field bump within the cavity to shapethe orbits of the particles in order to direct the orbits of particlesto the extraction channel. The example particle accelerator may includeone or more of the following features, either alone or in combination.

The magnetic field may be at least 4 Tesla or 8 Tesla. The magneticfield bump may be at most 2 Tesla. The regenerator may be movable in oneor more dimensions relative to the plasma column. The regenerator mayhave an irregular cross-sectional shape that is designed to produce amagnetic field bump have a specific shape and/or magnitude. Thecross-sectional irregular shape may include an angular feature on aportion of the regenerator facing towards the cavity, the angularfeature may include an edge comprising a non-orthogonal intersection oftwo faces. The example particle accelerator may include multipleregenerators of the type described herein configured and arranged in theorbital cavity to produce one or more magnetic field bumps and/or toshape the magnetic field bump(s).

The extraction channel may include a septum that separates particlesentering the extraction channel from particles remaining in the cavity.The regenerator may be configured so that a pitch and an angle of aparticle orbit enable a majority of particles in the particle orbit topass over the septum and into the extraction channel. The particle orbitpassing over the septum may include a range of radii of particlesrelative to the plasma column.

An example proton therapy system may include the foregoing particleaccelerator; and a gantry on which the particle accelerator is mounted.The gantry is rotatable relative to a patient position. Protons areoutput essentially directly from the particle accelerator to the patientposition. The particle accelerator may be a synch rocyclotron.

In an example, a particle accelerator includes: a voltage source toprovide a radio frequency (RF) voltage to a cavity to accelerateparticles from a plasma column, where the cavity has a magnetic fieldcausing particles accelerated from the plasma column to move orbitallywithin the cavity; an extraction channel to receive the particlesaccelerated from the plasma column and to output the received particlesfrom the cavity; and a regenerator to provide a magnetic field bumpwithin the cavity to thereby change successive orbits of the particlesaccelerated from the plasma column so that, eventually, particles outputto the extraction channel. The particle accelerator is configured tovary an energy of the particles that move orbitally within the cavity.The particle accelerator may include one or more of the followingfeatures, either alone or in combination.

The regenerator may be movable in one or more dimensions within thecavity, such that movement of the regenerator is correlated to an energyof the particles. The particle accelerator may include coils to passcurrent to generate the magnetic field, where a variation in the amountof current through the coils corresponds to a variation in an energy ofthe particles. The particle accelerator may include an energy degraderto affect an energy of a particle beam output from the particleaccelerator.

Two or more of the features described in this disclosure, includingthose described in this summary section, may be combined to formimplementations not specifically described herein.

Control of the various systems described herein, or portions thereof,may be implemented via a computer program product that includesinstructions that are stored on one or more non-transitorymachine-readable storage media, and that are executable on one or moreprocessing devices. The systems described herein, or portions thereof,may be implemented as an apparatus, method, or electronic system thatmay include one or more processing devices and memory to storeexecutable instructions to implement control of the stated functions.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example particle therapy system.

FIG. 2 is an exploded perspective view of example components of asynchrocyclotron.

FIGS. 3, 4, and 5 are cross-sectional views of an example synchrocyclotron.

FIG. 6 is a perspective view of an example synchrocyclotron.

FIG. 7 is a cross-sectional view of a portion of an example reversebobbin and windings.

FIG. 8 is a cross sectional view of an example cable-in-channelcomposite conductor.

FIG. 9 is a cross-sectional view of an example ion source.

FIG. 10 is a perspective view of an example dee plate and an exampledummy dee.

FIG. 11 is a perspective view of an example vault.

FIG. 12 is a perspective view of an example treatment room with a vault.

FIG. 13 shows a patient positioned next to a particle accelerator.

FIG. 14 shows a patient positioned within an example inner gantry in atreatment room.

FIG. 15 is a top view of an example acceleration cavity and an exampleextraction channel.

FIG. 16 is a graph showing magnetic field strength versus radialdistance from a plasma column, along with a cross-section of an examplepart of a cryostat of a superconducting magnet.

FIG. 17 is a top view of an example acceleration cavity and extractionchannel, which depicts orbits moving to enter the extraction channel.

FIG. 18 is a top view of an example acceleration cavity and regenerator,which depicts magnetic field lines in the cavity.

FIG. 19 is a graph showing magnetic field strength versus radialdistance from a plasma column for a particle accelerator having abackground magnetic field of about 2 Tesla.

FIG. 20 is a top view of an example acceleration cavity having multipleaxially-aligned regenerators.

FIG. 21 is a cut-away side view of an example regenerator.

FIG. 22 is a front view of part of an extraction channel.

FIG. 23 is a conceptual view of an example particle therapy system thatmay use a variable-energy particle accelerator.

FIG. 24 is an example graph showing energy and current for variations inmagnetic field and distance in a particle accelerator.

FIG. 25 is a side view of an example structure for sweeping voltage on adee plate over a frequency range for each energy level of a particlebeam, and for varying the frequency range when the particle beam energyis varied.

FIG. 26 is a perspective, exploded view of an example magnet system thatmay be used in a variable-energy particle accelerator.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION Overview

Described herein is an example of a particle accelerator for use in anexample system, such as a proton or ion therapy system. The systemincludes a particle accelerator—in this example, asynchrocyclotron—mounted on a gantry. The gantry enables the acceleratorto be rotated around a patient position, as explained in more detailbelow. In some implementations, the gantry is steel and has two legsmounted for rotation on two respective bearings that lie on oppositesides of a patient. The particle accelerator is supported by a steeltruss that is long enough to span a treatment area in which the patientlies and that is attached stably at both ends to the rotating legs ofthe gantry. As a result of rotation of the gantry around the patient,the particle accelerator also rotates.

In an example implementation, the particle accelerator (e.g., thesynchrocyclotron) includes a cryostat that holds a superconducting coilfor conducting a current that generates a magnetic field (B). In thisexample, the cryostat uses liquid helium (He) to maintain the coil atsuperconducting temperatures, e.g., 4° Kelvin (K). Magnetic yokes areadjacent (e.g., around) the cryostat, and define a cavity in whichparticles are accelerated. The cryostat is attached to the magneticyokes through straps or the like. While this attachment, and theattachment of the superconducting coil inside the cryostat, restrictsmovement of the superconducting coil, coil movement is not entirelyprevented.

In this example implementation, the particle accelerator includes aparticle source (e.g., a Penning Ion Gauge—PIG source) to provide aplasma column to the cavity. Hydrogen gas is ionized to produce theplasma column. A voltage source provides a radio frequency (RF) voltageto the cavity to accelerate particles from the plasma column. As noted,in this example, the particle accelerator is a synchrocyclotron.Accordingly, the RF voltage is swept across a range of frequencies toaccount for relativistic effects on the particles (e.g., increasingparticle mass) when extracting particles from the column. The magneticfield produced by the coil causes particles accelerated from the plasmacolumn to accelerate orbitally within the cavity. A magnetic fieldregenerator (“regenerator”) is positioned near the outside of the cavity(e.g., at an interior edge thereof) to adjust the existing magneticfield inside the cavity to thereby change locations (e.g., the pitch andangle) of successive orbits of the particles accelerated from the plasmacolumn so that, eventually, the particles output to an extractionchannel that passes through the yokes. The regenerator may increase themagnetic field at a point in the cavity (e.g., it may produce a magneticfield “bump” at an area of the cavity), thereby causing each successiveorbit of particles at that point to precess outwardly toward the entrypoint of the extraction channel until it reaches the extraction channel.The extraction channel receives particles accelerated from the plasmacolumn and outputs the received particles from the cavity.

In some implementations, the regenerator is a single ferromagneticarrangement that is configured to generate a magnetic field bump havinga specific size and shape. In this context, a single ferromagneticarrangement may be a single contiguous or physically connected structureor it can be two vertically-aligned, but physically unconnectedferromagnetic structures (e.g., one on each yoke) separated by emptyspace through which magnetic flux passes. In this context, verticalalignment includes alignment between yokes and includes anyappropriately aligned whole or part of the ferromagnetic structures.

The regenerator may be made of steel (which includes iron), in whichcase the magnetic field bump produced by the regenerator is, at most,about 2 Tesla. Other materials, however, may be used to produce magneticfield bumps that are more than, or less than, 2 Tesla. For example, insome implementations, the magnetic field bump is in the range of 0.5Tesla to 1 Tesla. The magnetic field already in the cavity (referred toas the “background magnetic field”) is at least 4 Tesla, 5 Tesla, or 6Tesla, and sometimes more (e.g., 8 Tesla, 8.5 Tesla, 9 Tesla, 9.5 Tesla,10 Tesla, 10.5 Tesla, or more). Consequently, the hole in the magneticfield bump produced by a regenerator that provides a 2 Tesla or lessmagnetic field bump is small compared to the background magnetic field.As a result, the overall impact of the hole on the particle orbits isless than is the case in particle accelerators that use smallerbackground magnetic fields (e.g., 2 Tesla). In other words, because thebackground magnetic field is so high in proportion to the magnetic fieldbump, the effects of the resulting hole in the magnetic field are lessthan in lower-field accelerators. As a result, in some implementations,a single ferromagnetic arrangement may be used as the magnetic fieldregenerator, thereby eliminating the need for additional, progressivelysmaller, radially-adjacent regenerators to add progressively smallermagnetic field bumps to fill-in other magnetic field holes.

Furthermore, the physical position of the regenerator within the cavitymay be adjustable to compensate for movement of the superconductingcoil. For example, computer-controlled actuators may be used to adjustthe position of the regenerator in one or more dimensions within thecavity based, e.g., on a rotational position of the particleaccelerator. By so adjusting the position of the regenerator, it may bepossible to position the regenerator so that the appropriate adjustmentto the magnetic field resulting from the regenerator impacts the properparticle orbits regardless of the rotational position of the particleaccelerator.

The magnetic field regenerator described herein may be used in a singleparticle accelerator, and any two or more of the features thereofdescribed herein may be combined in a single particle accelerator. Theparticle accelerator may be used in any type of medical or non-medicalapplication. An example of a particle therapy system in which themagnetic field regenerator described herein may be used is providedbelow.

Example Particle Therapy System

Referring to FIG. 1, a charged particle radiation therapy system 500includes a beam-producing particle accelerator 502 having a weight andsize small enough to permit it to be mounted on a rotating gantry 504with its output directed straight (that is, essentially directly) fromthe accelerator housing toward a patient 506.

In some implementations, the steel gantry has two legs 508, 510 mountedfor rotation on two respective bearings 512, 514 that lie on oppositesides of the patient. The accelerator is supported by a steel truss 516that is long enough to span a treatment area 518 in which the patientlies (e.g., twice as long as a tall person, to permit the person to berotated fully within the space with any desired target area of thepatient remaining in the line of the beam) and is attached stably atboth ends to the rotating legs of the gantry.

In some examples, the rotation of the gantry is limited to a range 520of less than 360 degrees, e.g., about 180 degrees, to permit a floor 522to extend from a wall of the vault 524 that houses the therapy systeminto the patient treatment area. The limited rotation range of thegantry also reduces the required thickness of some of the walls, whichprovide radiation shielding of people outside the treatment area. Arange of 180 degrees of gantry rotation is enough to cover all treatmentapproach angles, but providing a larger range of travel can be useful.For example the range of rotation may be between 180 and 330 degrees andstill provide clearance for the therapy floor space.

The horizontal rotational axis 532 of the gantry is located nominallyone meter above the floor where the patient and therapist interact withthe therapy system. This floor is positioned about 3 meters above thebottom floor of the therapy system shielded vault. The accelerator canswing under the raised floor for delivery of treatment beams from belowthe rotational axis. The patient couch moves and rotates in asubstantially horizontal plane parallel to the rotational axis of thegantry. The couch can rotate through a range 534 of about 270 degrees inthe horizontal plane with this configuration. This combination of gantryand patient rotational ranges and degrees of freedom allow the therapistto select virtually any approach angle for the beam. If needed, thepatient can be placed on the couch in the opposite orientation and thenall possible angles can be used.

In some implementations, the accelerator uses a synchrocyclotronconfiguration having a very high magnetic field superconductingelectromagnetic structure. Because the bend radius of a charged particleof a given kinetic energy is reduced in direct proportion to an increasein the magnetic field applied to it, the very high magnetic fieldsuperconducting magnetic structure permits the accelerator to be madesmaller and lighter. The synchrocyclotron uses a magnetic field that isuniform in rotation angle and falls off in strength with increasingradius. Such a field shape can be achieved regardless of the magnitudeof the magnetic field, so in theory there is no upper limit to themagnetic field strength (and therefore the resulting particle energy ata fixed radius) that can be used in a synchrocyclotron.

Superconducting materials lose their superconducting properties in thepresence of very high magnetic fields. High performance superconductingwire windings are used to allow very high magnetic fields to beachieved.

Superconducting materials typically need to be cooled to lowtemperatures for their superconducting properties to be realized. Insome examples described here, cryo-coolers are used to bring thesuperconducting coil windings to temperatures near absolute zero. Usingcryo-coolers can reduce complexity and cost.

The synchrocyclotron is supported on the gantry so that the beam isgenerated directly in line with the patient. The gantry permits rotationof the cyclotron about a horizontal rotational axis that contains apoint (isocenter 540) within, or near, the patient. The split truss thatis parallel to the rotational axis, supports the cyclotron on bothsides.

Because the rotational range of the gantry is limited, a patient supportarea can be accommodated in a wide area around the isocenter. Becausethe floor can be extended broadly around the isocenter, a patientsupport table can be positioned to move relative to and to rotate abouta vertical axis 542 through the isocenter so that, by a combination ofgantry rotation and table motion and rotation, any angle of beamdirection into any part of the patient can be achieved. The two gantryarms are separated by more than twice the height of a tall patient,allowing the couch with patient to rotate and translate in a horizontalplane above the raised floor.

Limiting the gantry rotation angle allows for a reduction in thethickness of at least one of the walls surrounding the treatment room.Thick walls, typically constructed of concrete, provide radiationprotection to individuals outside the treatment room. A wall downstreamof a stopping proton beam may be about twice as thick as a wall at theopposite end of the room to provide an equivalent level of protection.Limiting the range of gantry rotation enables the treatment room to besited below earth grade on three sides, while allowing an occupied areaadjacent to the thinnest wall reducing the cost of constructing thetreatment room.

In the example implementation shown in FIG. 1, the superconductingsynchrocyclotron 502 operates with a peak magnetic field in a pole gapof the synchrocyclotron of 8.8 Tesla. The synchrocyclotron produces abeam of protons having an energy of 250 MeV. In other implementationsthe field strength could be in the range of 4 to 20 Tesla or 6 to 20Tesla and the proton energy could be in the range of 150 to 300 MeV

The radiation therapy system described in this example is used forproton radiation therapy, but the same principles and details can beapplied in analogous systems for use in heavy ion (ion) treatmentsystems.

As shown in FIGS. 2, 3, 4, 5, and 6, an example synchrocyclotron 10(e.g., 502 in FIG. 1) includes a magnet system 12 that contains anparticle source 90, a radiofrequency drive system 91, and a beamextraction system 38. The magnetic field established by the magnetsystem has a shape appropriate to maintain focus of a contained protonbeam using a combination of a split pair of annular superconductingcoils 40, 42 and a pair of shaped ferromagnetic (e.g., low carbon steel)pole faces 44, 46.

The two superconducting magnet coils are centered on a common axis 47and are spaced apart along the axis. As shown in FIGS. 7 and 8, thecoils are formed by of Nb₃Sn-based superconducting 0.8 mm diameterstrands 48 (that initially comprise a niobium-tin core surrounded by acopper sheath) deployed in a twisted cable-in-channel conductorgeometry. After seven individual strands are cabled together, they areheated to cause a reaction that forms the final (brittle)superconducting material of the wire. After the material has beenreacted, the wires are soldered into the copper channel (outerdimensions 3.18×2.54 mm and inner dimensions 2.08×2.08 mm) and coveredwith insulation 52 (in this example, a woven fiberglass material). Thecopper channel containing the wires 53 is then wound in a coil having arectangular cross-section of 8.55 cm×19.02 cm, having 26 layers and 49turns per layer. The wound coil is then vacuum impregnated with an epoxycompound. The finished coils are mounted on an annular stainless steelreverse bobbin 56. Heater blankets 55 are placed at intervals in thelayers of the windings to protect the assembly in the event of a magnetquench.

The entire coil can then be covered with copper sheets to providethermal conductivity and mechanical stability and then contained in anadditional layer of epoxy. The precompression of the coil can beprovided by heating the stainless steel reverse bobbin and fitting thecoils within the reverse bobbin. The reverse bobbin inner diameter ischosen so that when the entire mass is cooled to 4 K, the reverse bobbinstays in contact with the coil and provides some compression. Heatingthe stainless steel reverse bobbin to approximately 50 degrees C. andfitting coils at a temperature of 100 degrees Kelvin can achieve this.

The geometry of the coil is maintained by mounting the coils in areverse rectangular bobbin 56 to exert a restorative force 60 that worksagainst the distorting force produced when the coils are energized. Asshown in FIG. 5, the coil position is maintained relative to the magnetyoke and cryostat using a set of warm-to-cold support straps 402, 404,406. Supporting the cold mass with thin straps reduces the heat leakageimparted to the cold mass by the rigid support system. The straps arearranged to withstand the varying gravitational force on the coil as themagnet rotates on board the gantry. They withstand the combined effectsof gravity and the large de-centering force realized by the coil when itis perturbed from a perfectly symmetric position relative to the magnetyoke. Additionally the links act to reduce dynamic forces imparted onthe coil as the gantry accelerates and decelerates when its position ischanged. Each warm-to-cold support includes one S2 fiberglass link andone carbon fiber link. The carbon fiber link is supported across pinsbetween the warm yoke and an intermediate temperature (50-70 K), and theS2 fiberglass link 408 is supported across the intermediate temperaturepin and a pin attached to the cold mass. Each link is 5 cm long (pincenter to pin center) and is 17 mm wide. The link thickness is 9 mm.Each pin is made of high strength stainless steel and is 40 mm indiameter.

Referring to FIG. 3, the field strength profile as a function of radiusis determined largely by choice of coil geometry and pole face shape;the pole faces 44, 46 of the permeable yoke material can be contoured tofine tune the shape of the magnetic field to ensure that the particlebeam remains focused during acceleration.

The superconducting coils are maintained at temperatures near absolutezero (e.g., about 4 degrees Kelvin) by enclosing the coil assembly (thecoils and the bobbin) inside an evacuated annular aluminum or stainlesssteel cryostatic chamber 70 that provides a free space around the coilstructure, except at a limited set of support points 71, 73. In analternate version (FIG. 4) the outer wall of the cryostat may be made oflow carbon steel to provide an additional return flux path for themagnetic field.

In some implementations, the temperature near absolute zero is achievedand maintained using one single-stage Gifford-McMahon cryo-cooler andthree two-stage Gifford McMahon cryo-coolers. Each two stage cryo-coolerhas a second stage cold end attached to a condenser that recondensesHelium vapor into liquid Helium. The cryo-cooler heads are supplied withcompressed Helium from a compressor. The single-stage Gifford-McMahoncryo-cooler is arranged to cool high temperature (e.g., 50-70 degreesKelvin) leads that supply current to the superconducting windings.

In some implementations, the temperature near absolute zero is achievedand maintained using two Gifford-McMahon cryo-coolers 72, 74 that arearranged at different positions on the coil assembly. Each cryo-coolerhas a cold end 76 in contact with the coil assembly. The cryo-coolerheads 78 are supplied with compressed Helium from a compressor 80. Twoother Gifford-McMahon cryo-coolers 77, 79 are arranged to cool hightemperature (e.g., 60-80 degrees Kelvin) leads that supply current tothe superconducting windings.

The coil assembly and cryostatic chambers are mounted within and fullyenclosed by two halves 81, 83 of a pillbox-shaped magnet yoke 82. Inthis example, the inner diameter of the coil assembly is about 74.6 cm.The iron yoke 82 provides a path for the return magnetic field flux 84and magnetically shields the volume 86 between the pole faces 44, 46 toprevent external magnetic influences from perturbing the shape of themagnetic field within that volume. The yoke also serves to decrease thestray magnetic field in the vicinity of the accelerator. In someimplementations, the synchrocyclotron may have an active return systemto reduce stray magnetic fields. An example of an active return systemis described in U.S. patent application Ser. No. 13/907,601, which wasfiled on May 31, 2013, the contents of which are incorporated herein byreference. In the active return system, the relatively large magneticyokes described herein are replaced by smaller magnetic structures,referred to as pole pieces. Superconducting coils run current oppositeto the main coils described herein in order to provide magnetic returnand thereby reduce stray magnetic fields

As shown in FIGS. 3 and 9, the synchrocyclotron includes a particlesource 90 of a Penning ion gauge geometry located near the geometriccenter 92 of the magnet structure 82. The particle source may be asdescribed below, or the particle source may be of the type described inU.S. patent application Ser. No. 11/948,662 incorporated herein byreference.

Particle source 90 is fed from a supply 99 of hydrogen through a gasline 101 and tube 194 that delivers gaseous hydrogen. Electric cables 94carry an electric current from a current source 95 to stimulate electrondischarge from cathodes 192, 190 that are aligned with the magneticfield, 200.

In some implementations, the gas in gas tube 101 may include a mixtureof hydrogen and one or more other gases. For example, the mixture maycontain hydrogen and one or more of the noble gases, e.g., helium, neon,argon, krypton, xenon and/or radon (although the mixture is not limitedto use with the noble gases). In some implementations, the mixture maybe a mixture of hydrogen and helium. For example, the mixture maycontain about 75% or more of hydrogen and about 25% or less of helium(with possible trace gases included). In another example, the mixturemay contain about 90% or more of hydrogen and about 10% or less ofhelium (with possible trace gases included). In examples, thehydrogen/helium mixture may be any of thefollowing: >95%/1<5%, >90%/<10%, >85%/<15%, >80%/<20%, >75%/<20%, and soforth.

Possible advantages of using a noble (or other) gas in combination withhydrogen in the particle source may include: increased beam intensity,increased cathode longevity, and increased consistency of beam output.

In this example, the discharged electrons ionize the gas exiting througha small hole from tube 194 to create a supply of positive ions (protons)for acceleration by one semicircular (dee-shaped) radio-frequency plate100 that spans half of the space enclosed by the magnet structure andone dummy dee plate 102. In the case of an interrupted particle source(an example of which is described in U.S. patent application Ser. No.11/948,662), all (or a substantial part) of the tube containing plasmais removed at the acceleration region, thereby allowing ions to be morerapidly accelerated in a relatively high magnetic field.

As shown in FIG. 10, the dee plate 100 is a hollow metal structure thathas two semicircular surfaces 103, 105 that enclose a space 107 in whichthe protons are accelerated during half of their rotation around thespace enclosed by the magnet structure. A duct 109 opening into thespace 107 extends through the yoke to an external location from which avacuum pump 111 can be attached to evacuate the space 107 and the restof the space within a vacuum chamber 119 in which the acceleration takesplace. The dummy dee 102 comprises a rectangular metal ring that isspaced near to the exposed rim of the dee plate. The dummy dee isgrounded to the vacuum chamber and magnet yoke. The dee plate 100 isdriven by a radio-frequency signal that is applied at the end of aradio-frequency transmission line to impart an electric field in thespace 107. The radio frequency electric field is made to vary in time asthe accelerated particle beam increases in distance from the geometriccenter. The radio frequency electric field may be controlled in themanner described in U.S. patent application Ser. No. 11/948,359,entitled “Matching A Resonant Frequency Of A Resonant Cavity To AFrequency Of An Input Voltage”, the contents of which are incorporatedherein by reference.

For the beam emerging from the centrally located particle source toclear the particle source structure as it begins to spiral outward, alarge voltage difference is required across the radio frequency plates.20,000 Volts is applied across the radio frequency plates. In someversions from 8,000 to 20,000 Volts may be applied across the radiofrequency plates. To reduce the power required to drive this largevoltage, the magnet structure is arranged to reduce the capacitancebetween the radio frequency plates and ground. This is done by formingholes with sufficient clearance from the radio frequency structuresthrough the outer yoke and the cryostat housing and making sufficientspace between the magnet pole faces.

The high voltage alternating potential that drives the dee plate has afrequency that is swept downward during the accelerating cycle toaccount for the increasing relativistic mass of the protons and thedecreasing magnetic field. The dummy dee does not require a hollowsemi-cylindrical structure as it is at ground potential along with thevacuum chamber walls. Other plate arrangements could be used such asmore than one pair of accelerating electrodes driven with differentelectrical phases or multiples of the fundamental frequency. The RFstructure can be tuned to keep the Q high during the required frequencysweep by using, for example, a rotating capacitor having intermeshingrotating and stationary blades. During each meshing of the blades, thecapacitance increases, thus lowering the resonant frequency of the RFstructure. The blades can be shaped to create a precise frequency sweeprequired. A drive motor for the rotating condenser can be phase lockedto the RF generator for precise control. One bunch of particles isaccelerated during each meshing of the blades of the rotating condenser.

The vacuum chamber 119 in which the acceleration occurs is a generallycylindrical container that is thinner in the center and thicker at therim. The vacuum chamber encloses the RF plates and the particle sourceand is evacuated by the vacuum pump 111. Maintaining a high vacuuminsures that accelerating ions are not lost to collisions with gasmolecules and enables the RF voltage to be kept at a higher levelwithout arcing to ground.

Protons traverse a generally spiral orbital path beginning at theparticle source. In half of each loop of the spiral path, the protonsgain energy as they pass through the RF electric field in space 107. Asthe ions gain energy, the radius of the central orbit of each successiveloop of their spiral path is larger than the prior loop until the loopradius reaches the maximum radius of the pole face. At that location amagnetic and electric field perturbation directs ions into an area wherethe magnetic field rapidly decreases, and the ions depart the area ofthe high magnetic field and are directed through an evacuated tube 38,referred to herein as the extraction channel, to exit the yoke of thecyclotron. A magnetic regenerator may be used to change the magneticfield perturbation to direct the ions. The ions exiting the cyclotronwill tend to disperse as they enter the area of markedly decreasedmagnetic field that exists in the room around the cyclotron. Beamshaping elements 107, 109 in the extraction channel 38 redirect the ionsso that they stay in a straight beam of limited spatial extent.

The magnetic field within the pole gap needs to have certain propertiesto maintain the beam within the evacuated chamber as it accelerates. Themagnetic field index n, which is shown below,n=−(r/B)dB/dr,should be kept positive to maintain this “weak” focusing. Here r is theradius of the beam and B is the magnetic field. Additionally, in someimplementations, the field index needs to be maintained below 0.2,because at this value the periodicity of radial oscillations andvertical oscillations of the beam coincide in a vr=2 v_(z) resonance.The betatron frequencies are defined by v_(r)=(1−n)^(1/2) andv_(z)=n^(1/2). The ferromagnetic pole face is designed to shape themagnetic field generated by the coils so that the field index n ismaintained positive and less than 0.2 in the smallest diameterconsistent with a 250 MeV beam in the given magnetic field.

As the beam exits the extraction channel it is passed through a beamformation system 125 (FIG. 5) that can be programmably controlled tocreate a desired combination of scattering angle and range modulationfor the beam. Beam formation system 125 may be used in conjunction withan inner gantry 601 (FIG. 14) to direct a beam to the patient.

During operation, the plates absorb energy from the applied radiofrequency field as a result of conductive resistance along the surfacesof the plates. This energy appears as heat and is removed from theplates using water cooling lines 108 that release the heat in a heatexchanger 113 (FIG. 3).

Stray magnetic fields exiting from the cyclotron are limited by both thepillbox magnet yoke (which also serves as a shield) and a separatemagnetic shield 114. The separate magnetic shield includes of a layer117 of ferromagnetic material (e.g., steel or iron) that encloses thepillbox yoke, separated by a space 116. This configuration that includesa sandwich of a yoke, a space, and a shield achieves adequate shieldingfor a given leakage magnetic field at lower weight.

As mentioned, the gantry allows the synchrocyclotron to be rotated aboutthe horizontal rotational axis 532. The truss structure 516 has twogenerally parallel spans 580, 582. The synchrocyclotron is cradledbetween the spans about midway between the legs. The gantry is balancedfor rotation about the bearings using counterweights 122, 124 mounted onends of the legs opposite the truss.

The gantry is driven to rotate by an electric motor mounted to one orboth of the gantry legs and connected to the bearing housings by drivegears. The rotational position of the gantry is derived from signalsprovided by shaft angle encoders incorporated into the gantry drivemotors and the drive gears.

At the location at which the ion beam exits the cyclotron, the beamformation system 125 acts on the ion beam to give it properties suitablefor patient treatment. For example, the beam may be spread and its depthof penetration varied to provide uniform radiation across a given targetvolume. The beam formation system can include passive scatteringelements as well as active scanning elements.

All of the active systems of the synchrocyclotron (the current drivensuperconducting coils, the RF-driven plates, the vacuum pumps for thevacuum acceleration chamber and for the superconducting coil coolingchamber, the current driven particle source, the hydrogen gas source,and the RF plate coolers, for example), may be controlled by appropriatesynchrocyclotron control electronics (not shown), which may include,e.g., one or more computers programmed with appropriate programs toeffect control.

The control of the gantry, the patient support, the active beam shapingelements, and the synchrocyclotron to perform a therapy session isachieved by appropriate therapy control electronics (not shown).

As shown in FIGS. 1, 11, and 12, the gantry bearings are supported bythe walls of a cyclotron vault 524. The gantry enables the cyclotron tobe swung through a range 520 of 180 degrees (or more) includingpositions above, to the side of, and below the patient. The vault istall enough to clear the gantry at the top and bottom extremes of itsmotion. A maze 146 sided by walls 148, 150 provides an entry and exitroute for therapists and patients. Because at least one wall 152 is notin line with the proton beam directly from the cyclotron, it can be maderelatively thin and still perform its shielding function. The otherthree side walls 154, 156, 150/148 of the room, which may need to bemore heavily shielded, can be buried within an earthen hill (not shown).The required thickness of walls 154, 156, and 158 can be reduced,because the earth can itself provide some of the needed shielding.

Referring to FIGS. 12 and 13, for safety and aesthetic reasons, atherapy room 160 may be constructed within the vault. The therapy roomis cantilevered from walls 154, 156, 150 and the base 162 of thecontaining room into the space between the gantry legs in a manner thatclears the swinging gantry and also maximizes the extent of the floorspace 164 of the therapy room. Periodic servicing of the accelerator canbe accomplished in the space below the raised floor. When theaccelerator is rotated to the down position on the gantry, full accessto the accelerator is possible in a space separate from the treatmentarea. Power supplies, cooling equipment, vacuum pumps and other supportequipment can be located under the raised floor in this separate space.Within the treatment room, the patient support 170 can be mounted in avariety of ways that permit the support to be raised and lowered and thepatient to be rotated and moved to a variety of positions andorientations.

In system 602 of FIG. 14, a beam-producing particle accelerator of thetype described herein, in this case synchrocyclotron 604, is mounted onrotating gantry 605. Rotating gantry 605 is of the type describedherein, and can angularly rotate around patient support 606. Thisfeature enables synchrocyclotron 604 to provide a particle beam directlyto the patient from various angles. For example, as in FIG. 14, ifsynchrocyclotron 604 is above patient support 606, the particle beam maybe directed downwards toward the patient. Alternatively, ifsynchrocyclotron 604 is below patient support 606, the particle beam maybe directed upwards toward the patient. The particle beam is applieddirectly to the patient in the sense that an intermediary beam routingmechanism is not required. A routing mechanism, in this context, isdifferent from a shaping or sizing mechanism in that a shaping or sizingmechanism does not re-route the beam, but rather sizes and/or shapes thebeam while maintaining the same general trajectory of the beam.

Further details regarding an example implementation of the foregoingsystem may be found in U.S. Pat. No. 7,728,311, filed on Nov. 16, 2006and entitled “Charged Particle Radiation Therapy”, and in U.S. patentapplication Ser. No. 12/275,103, filed on Nov. 20, 2008 and entitled“Inner Gantry”. The contents of U.S. Pat. No. 7,728,311 and in U.S.patent application Ser. No. 12/275,103 are hereby incorporated byreference into this disclosure. In some implementations, thesynchrocyclotron may be a variable-energy device, such as that describedbelow and in U.S. patent application Ser. No. 13/916,401, filed on Jun.12, 2013, the contents of which are incorporated herein by reference.

Example Implementations

FIG. 15 shows a top view of a portion of a cavity 700 in which particlesare accelerated orbitally (e.g., in outward spiral orbits). A particlesource 701, examples of which are described above, is disposed at aboutthe center of the cavity. Charged particles (e.g., protons or ions) areextracted from a plasma column generated by particle source 701. Thecharged particles accelerate outwardly in orbits toward, and eventuallyreaching, magnetic field regenerator 702. In this exampleimplementation, regenerator 702 is a single ferromagnetic arrangementmade, e.g., of steel, iron, or any other type of ferromagnetic material.Regenerator 702 may include portions thereof connected to respectivehalves of each magnetic yoke. Regenerator 702 alters the backgroundmagnetic field that causes the outward orbital acceleration. In thisexample, regenerator 702 augments that magnetic field, e.g., it providesa bump in the field by enhancing the magnetic field at its location. Thebump in the background magnetic field affects the particle orbits in away that causes the orbits to move outwardly towards extraction channel703. Eventually, the orbits enter extraction channel 703, from whichthey exit.

In more detail, a particle beam orbit approaches and interacts withregenerator 702. As a result of the increased magnetic field, theparticle beam turns a bit more there and, instead of being circular, itprecesses to the extraction channel. FIG. 16 shows the magnetic field(B) plotted against the radius (r) relative to the particle source 702.As shown in FIG. 16, in this example, B varies from about 9 Tesla (T) toabout −2 T. In other implementations, the magnetic field may vary fromabout 4 T, 5 T, 6 T, 7 T, 8 T, 8.5 T, 9.5 T, 10 T, 105 T, and so forthto −2 T or other values. In this implementation, the 9 T occurs at aboutthe center of cavity 700. The polarity of the magnetic field changesafter the magnetic field crosses the superconducting coil, resulting inabout −2 T on the exterior of the coil, eventually fading to about zero.The magnetic field bump 705 occurs at the point of the regenerator. FIG.16 also shows the magnetic field plot relative to a cross-section of abobbin 706 having extraction channel 703 between two superconductingcoils 709, 710.

FIG. 18 shows magnetic effects of the regenerator. More specifically, asshown in FIG. 18, regenerator 702 produces a magnetic field depicted bymagnetic field lines 750. Magnetic field lines 750 create a magnetichole 753 in the background magnetic field. This hole is also depicted inFIG. 16. More specifically, as noted above, FIG. 16 shows magnetic fieldbump 705 (e.g., 0.5 T to 2 T) produced by regenerator 702, along withthe corresponding hole 753 in the background magnetic field. As shown,hole 753 is relatively small in comparison to the background magneticfield. As such, its effect on precession of the orbits is relativelysmall. As a result, a single regenerator can be used havingcharacteristics similar to those described herein. By contrast,referring to FIG. 19, in a particle accelerator having about 2 T ofbackground magnetic field, the resulting hole 755 would be significantrelative to the background magnetic field. Accordingly, progressivelysmaller ferromagnetic structures are added to produce progressivelysmaller magnetic field bumps to fill-in hole 755 and additional holescreated by the progressively smaller ferromagnetic structures.

In this regard, as explained above, in some implementations, regenerator702 is a single vertically-aligned ferromagnetic (e.g., steel)arrangement that produces a magnetic field bump of at most 2 T in thepresence of a background magnetic field of at least 4 T, 5 T, 6 T (ormore, e.g., 7 T, 8 T, 8.5 T, 9.5 T, 10 T, 105 T, and so forth). In someimplementations, however, there may be more than one regenerator. Eachregenerator may be a progressively smaller, substantiallyradially-adjacent ferromagnetic arrangement, as shown in FIG. 20, in thepresence of magnetic fields of 4 T, 5 T, 6 T or greater (where theradius is from the plasma column outward). In the example of FIG. 20,cavity 760 includes multiple regenerators 761 to 764 relative to plasmacolumn 765. In some implementations, these additional regenerators neednot be progressively smaller in size. For example, each one may have thesame, or similar size, but may be made of material that produces asmaller magnetic field bump closer to the plasma column. For example,the outermost regenerator relative to the plasma column may have thehighest percentage of ferromagnetic material; the next regeneratorinward may have a lesser percentage of ferromagnetic material, and soforth. Combinations of size and percentage of ferromagnetic material maybe combined to produce the desire effects. Accordingly, the particleaccelerator is not limited to use with a regenerator that comprises asingle ferromagnetic arrangement, but rather may also be used withmultiple, radially-adjacent magnetic field regenerators.

As noted, in some example implementations, a particle accelerator mayinclude multiple regenerators of the type described herein configuredand arranged in the orbital cavity to produce one or more magnetic fieldbumps and/or to shape the magnetic field bump(s). Two or more of thesemultiple regenerators may be radially-aligned, axially-aligned, or notaligned.

The regenerator may be configured (e.g., shaped and/or moved) togenerate a magnetic field bump having any appropriate size (e.g.,magnitude) and shape. In some implementations, portions of theregenerator have an irregular cross-sectional shape that is designed toproduce a magnetic field bump have a specific shape and/or magnitude. Anexample of such a cross sectional shape 770 for a portion of regenerator702 is shown in FIG. 21. There, the cross-sectional irregular shapecomprises an angular feature 771 on a portion of the regenerator facingtowards the cavity. As shown, angular feature 771 is an edge comprisinga non-orthogonal intersection of two faces 772, 773. In otherimplementations, the cross-sectional shape of a portion of theregenerator may be another irregular shape or may be rectangular,square, curved, trapezoidal, triangular, and so forth. In this example,each cross-section of regenerator 702 is physically connected to acorresponding half yoke 81, 83.

Referring to FIG. 17, regenerator 702 causes changes in the angle 780and pitch 781 of orbits 710 so that they move toward extraction channel703. At the point of the extraction channel, the magnetic field strengthis sufficiently low to enable the particle beam to enter the extractionchannel and to proceed therethrough. Referring back to FIG. 15,extraction channel 703 contains various magnetic structures 711 foradding and/or subtracting dipole fields to direct the entering particlebeam through extraction channel 703, to beam shaping elements.

Referring to FIG. 22, in some implementations extraction channel 703includes a septum 775 near its entry point that separates particles 776entering the extraction channel from particles 777 remaining in thecavity. The regenerator is configured so that a pitch and an angle of aparticle orbit enable a majority of particles in the particle orbit topass over the septum and into the extraction channel. Particles that hitseptum are typically lost. Accordingly, the regenerator may beconfigured (e.g., shaped and/or moved) to increase the number ofparticles in a particular orbit that enter the extraction channel andthereby decrease the number of particles that hit the septum. However,in some implementations, even in best case scenarios, there will beparticles that hit the septum and that are lost.

In some implementations, regenerator 702 may be moved so that, atdifferent rotational positions, the regenerator affects differentparticle orbits. The effective magnetic center of the regenerator fieldbump may also be moved with ferromagnetic elements actuated adjacent toa fixed regenerator. As above, the movement or regenerator 702 orresulting magnetic field perturbation may be computer-controlled througha control system that is part of the particle therapy system. Forexample, the movement of regenerator 702 may be controlled based on arotational position of the particle accelerator, as measured by therotational position of the gantry on which the particle accelerator ismounted. The various parameters used to set the location of theregenerator vis-à-vis the rotational position of the gantry may bemeasured empirically, and programmed into the control system computer.One or more computer-controlled actuators may effect actual movement ofthe regenerator.

The regenerator may be moved in any appropriate direction to affect themagnetic field. For example, the regenerator may be moved in the radialdirection (e.g., towards or away-from, the particle source). Theregenerator may be moved in the Cartesian X, Y and/or Z directions(e.g., length-wise, width-wise or depth-wise) within the cavity in orderto provide the appropriate changes to the magnetic field. Theregenerator may be rotated relative to its original position to providethe appropriate magnetic field changes.

Variable-Energy Particle Accelerator

The particle accelerator used in the example particle therapy systemsdescribed herein may be a variable-energy particle accelerator.

The energy of the extracted particle beam (the particle beam output fromthe accelerator) can affect the use of the particle beam duringtreatment. In some machines, the energy of the particle beam (orparticles in the particle beam) does not increase after extraction.However, the energy may be reduced based on treatment needs after theextraction and before the treatment. Referring to FIG. 23, an exampletreatment system 810 includes an accelerator 812, e.g., asynchrocyclotron, from which a particle (e.g., proton) beam 814 having avariable energy is extracted to irradiate a target volume 824 of a body822. Optionally, one or more additional devices, such as a scanning unit816 or a scattering unit 816, one or more monitoring units 818, and anenergy degrader 820, are placed along the irradiation direction 828. Thedevices intercept the cross-section of the extracted beam 814 and alterone or more properties of the extracted beam for the treatment.

A target volume to be irradiated (an irradiation target) by a particlebeam for treatment typically has a three-dimensional configuration. Insome examples, to carry-out the treatment, the target volume is dividedinto layers along the irradiation direction of the particle beam so thatthe irradiation can be done on a layer-by-layer basis. For certain typesof particles, such as protons, the penetration depth (or which layer thebeam reaches) within the target volume is largely determined by theenergy of the particle beam. A particle beam of a given energy does notreach substantially beyond a corresponding penetration depth for thatenergy. To move the beam irradiation from one layer to another layer ofthe target volume, the energy of the particle beam is changed.

In the example shown in FIG. 23, the target volume 824 is divided intonine layers 826 a-826 i along the irradiation direction 828. In anexample process, the irradiation starts from the deepest layer 826 i,one layer at a time, gradually to the shallower layers and finishes withthe shallowest layer 826 a. Before application to the body 822, theenergy of the particle beam 814 is controlled to be at a level to allowthe particle beam to stop at a desired layer, e.g., the layer 826 d,without substantially penetrating further into the body or the targetvolume, e.g., the layers 826 e-826 i or deeper into the body. In someexamples, the desired energy of the particle beam 814 decreases as thetreatment layer becomes shallower relative to the particle acceleration.In some examples, the beam energy difference for treating adjacentlayers of the target volume 824 is about 3 MeV to about 100 MeV, e.g.,about 10 MeV to about 80 MeV, although other differences may also bepossible, depending on, e.g., the thickness of the layers and theproperties of the beam.

The energy variation for treating different layers of the target volume824 can be performed at the accelerator 812 (e.g., the accelerator canvary the energy) so that, in some implementations, no additional energyvariation is required after the particle beam is extracted from theaccelerator 812. So, the optional energy degrader 820 in the treatmentsystem 10 may be eliminated from the system. In some implementations,the accelerator 812 can output particle beams having an energy thatvaries between about 100 MeV and about 300 MeV, e.g., between about 115MeV and about 250 MeV. The variation can be continuous ornon-continuous, e.g., one step at a time. In some implementations, thevariation, continuous or non-continuous, can take place at a relativelyhigh rate, e.g., up to about 50 MeV per second or up to about 20 MeV persecond. Non-continuous variation can take place one step at a time witha step size of about 10 MeV to about 80 MeV.

When irradiation is complete in one layer, the accelerator 812 can varythe energy of the particle beam for irradiating a next layer, e.g.,within several seconds or within less than one second. In someimplementations, the treatment of the target volume 824 can be continuedwithout substantial interruption or even without any interruption. Insome situations, the step size of the non-continuous energy variation isselected to correspond to the energy difference needed for irradiatingtwo adjacent layers of the target volume 824. For example, the step sizecan be the same as, or a fraction of, the energy difference.

In some implementations, the accelerator 812 and the degrader 820collectively vary the energy of the beam 814. For example, theaccelerator 812 provides a coarse adjustment and the degrader 820provides a fine adjustment or vice versa. In this example, theaccelerator 812 can output the particle beam that varies energy with avariation step of about 10-80 MeV, and the degrader 820 adjusts (e.g.,reduces) the energy of the beam at a variation step of about 2-10 MeV.

The reduced use (or absence) of the energy degrader, which can includerange shifters, helps to maintain properties and quality of the outputbeam from the accelerator, e.g., beam intensity. The control of theparticle beam can be performed at the accelerator. Side effects, e.g.,from neutrons generated when the particle beam passes the degrader 820can be reduced or eliminated.

The energy of the particle beam 814 may be adjusted to treat anothertarget volume 830 in another body or body part 822′ after completingtreatment in target volume 824. The target volumes 824, 830 may be inthe same body (or patient), or may belong to different patients. It ispossible that the depth D of the target volume 830 from a surface ofbody 822′ is different from that of the target volume 824. Although someenergy adjustment may be performed by the degrader 820, the degrader 812may only reduce the beam energy and not increase the beam energy.

In this regard, in some cases, the beam energy required for treatingtarget volume 830 is greater than the beam energy required to treattarget volume 824. In such cases, the accelerator 812 may increase theoutput beam energy after treating the target volume 824 and beforetreating the target volume 830. In other cases, the beam energy requiredfor treating target volume 830 is less than the beam energy required totreat target volume 824. Although the degrader 820 can reduce theenergy, the accelerator 812 can be adjusted to output a lower beamenergy to reduce or eliminate the use of the degrader 820. The divisionof the target volumes 824, 830 into layers can be different or the same.And the target volume 830 can be treated similarly on a layer by layerbasis to the treatment of the target volume 824.

The treatment of the different target volumes 824, 830 on the samepatient may be substantially continuous, e.g., with the stop timebetween the two volumes being no longer than about 30 minutes or less,e.g., 25 minutes or less, 20 minutes or less, 15 minutes or less, 10minutes or less, 5 minutes or less, or 1 minute or less. As is explainedherein, the accelerator 812 can be mounted on a movable gantry and themovement of the gantry can move the accelerator to aim at differenttarget volumes. In some situations, the accelerator 812 can complete theenergy adjustment of the output beam 814 during the time the treatmentsystem makes adjustment (such as moving the gantry) after completing thetreatment of the target volume 824 and before starting treating thetarget volume 830. After the alignment of the accelerator and the targetvolume 830 is done, the treatment can begin with the adjusted, desiredbeam energy. Beam energy adjustment for different patients can also becompleted relatively efficiently. In some examples, all adjustments,including increasing/reducing beam energy and/or moving the gantry aredone within about 30 minutes, e.g., within about 25 minutes, withinabout 20 minutes, within about 15 minutes, within about 10 minutes orwithin about 5 minutes.

In the same layer of a target volume, an irradiation dose is applied bymoving the beam across the two-dimensional surface of the layer (whichis sometimes called scanning beam) using a scanning unit 816.Alternatively, the layer can be irradiated by passing the extracted beamthrough one or more scatterers of the scattering unit 16 (which issometimes called scattering beam).

Beam properties, such as energy and intensity, can be selected before atreatment or can be adjusted during the treatment by controlling theaccelerator 812 and/or other devices, such as the scanningunit/scatterer(s) 816, the degrader 820, and others not shown in thefigures. In this example implementation, as in the exampleimplementations described above, system 810 includes a controller 832,such as a computer, in communication with one or more devices in thesystem. Control can be based on results of the monitoring performed bythe one or more monitors 818, e.g., monitoring of the beam intensity,dose, beam location in the target volume, etc. Although the monitors 818are shown to be between the device 816 and the degrader 820, one or moremonitors can be placed at other appropriate locations along the beamirradiation path. Controller 832 can also store a treatment plan for oneor more target volumes (for the same patient and/or different patients).The treatment plan can be determined before the treatment starts and caninclude parameters, such as the shape of the target volume, the numberof irradiation layers, the irradiation dose for each layer, the numberof times each layer is irradiated, etc. The adjustment of a beamproperty within the system 810 can be performed based on the treatmentplan. Additional adjustment can be made during the treatment, e.g., whendeviation from the treatment plan is detected.

In some implementations, the accelerator 812 is configured to vary theenergy of the output particle beam by varying the magnetic field inwhich the particle beam is accelerated. In an example implementation,one or more sets of coils receives variable electrical current toproduce a variable magnetic field in the cavity. In some examples, oneset of coils receives a fixed electrical current, while one or moreother sets of coils receives a variable current so that the totalcurrent received by the coil sets varies. In some implementations, allsets of coils are superconducting. In other implementations, some setsof coils, such as the set for the fixed electrical current, aresuperconducting, while other sets of coils, such as the one or more setsfor the variable current, are non-superconducting. In some examples, allsets of coils are non-superconducting.

Generally, the magnitude of the magnetic field is scalable with themagnitude of the electrical current. Adjusting the total electriccurrent of the coils in a predetermined range can generate a magneticfield that varies in a corresponding, predetermined range. In someexamples, a continuous adjustment of the electrical current can lead toa continuous variation of the magnetic field and a continuous variationof the output beam energy. Alternatively, when the electrical currentapplied to the coils is adjusted in a non-continuous, step-wise manner,the magnetic field and the output beam energy also varies accordingly ina non-continuous (step-wise) manner. The scaling of the magnetic fieldto the current can allow the variation of the beam energy to be carriedout relatively precisely, although sometimes minor adjustment other thanthe input current may be performed.

In some implementations, to output particle beams having a variableenergy, the accelerator 812 is configured to apply RF voltages thatsweep over different ranges of frequencies, with each rangecorresponding to a different output beam energy. For example, if theaccelerator 812 is configured to produce three different output beamenergies, the RF voltage is capable of sweeping over three differentranges of frequencies. In another example, corresponding to continuousbeam energy variations, the RF voltage sweeps over frequency ranges thatcontinuously change. The different frequency ranges may have differentlower frequency and/or upper frequency boundaries.

The extraction channel may be configured to accommodate the range ofdifferent energies produced by the variable-energy particle accelerator.Particle beams having different energies can be extracted from theaccelerator 812 without altering the features of the regenerator that isused for extracting particle beams having a single energy. In otherimplementations, to accommodate the variable particle energy, theregenerator can be moved to disturb (e.g., change) different particleorbits in the manner described above and/or iron rods (magnetic shims)can be added or removed to change the magnetic field bump provided bythe regenerator. More specifically, different particle energies willtypically be at different particle orbits within the cavity. By movingthe regenerator in the manner described herein, it is possible tointercept a particle orbit at a specified energy and thereby provide thecorrect perturbation of that orbit so that particles at the specifiedenergy reach the extraction channel. In some implementations, movementof the regenerator (and/or addition/removal of magnetic shims) isperformed in real-time to match real-time changes in the particle beamenergy output by the accelerator. In other implementations, particleenergy is adjusted on a per-treatment basis, and movement of theregenerator (and/or addition/removal of magnetic shims) is performed inadvance of the treatment. In either case, movement of the regenerator(and/or addition/removal of magnetic shims) may be computer controlled.For example, a computer may control one or more motors that effectmovement of the regenerator and/or magnetic shims.

In some implementations, the regenerator is implemented using one ormore magnetic shims that are controllable to move to the appropriatelocation(s).

As an example, table 1 shows three example energy levels at whichexample accelerator 812 can output particle beams. The correspondingparameters for producing the three energy levels are also listed. Inthis regard, the magnet current refers to the total electrical currentapplied to the one or more coil sets in the accelerator 812; the maximumand minimum frequencies define the ranges in which the RF voltagesweeps; and “r” is the radial distance of a location to a center of thecavity in which the particles are accelerated.

TABLE 1 Examples of beam energies and respective parameters. MagneticMagnetic Beam Magnet Maximum Minimum Field at Field at Energy CurrentFrequency Frequency r = 0 mm r = 298 mm (MeV) (Amps) (MHz) (MHz) (Tesla)(Tesla) 250 1990 132 99 8.7 8.2 235 1920 128 97 8.4 8.0 211 1760 120 937.9 7.5

Details that may be included in an example particle accelerator thatproduces charged particles having variable energies are described below.The accelerator can be a synchrocyclotron and the particles may beprotons. The particles output as pulsed beams. The energy of the beamoutput from the particle accelerator can be varied during the treatmentof one target volume in a patient, or between treatments of differenttarget volumes of the same patient or different patients. In someimplementations, settings of the accelerator are changed to vary thebeam energy when no beam (or particles) is output from the accelerator.The energy variation can be continuous or non-continuous over a desiredrange.

Referring to the example shown in FIG. 1, the particle accelerator(synchrocyclotron 502), which may be a variable-energy particleaccelerator like accelerator 812 described above, may be configured toparticle beams that have a variable energy. The range of the variableenergy can have an upper boundary that is about 200 MeV to about 300 MeVor higher, e.g., 200 MeV, about 205 MeV, about 210 MeV, about 215 MeV,about 220 MeV, about 225 MeV, about 230 MeV, about 235 MeV, about 240MeV, about 245 MeV, about 250 MeV, about 255 MeV, about 260 MeV, about265 MeV, about 270 MeV, about 275 MeV, about 280 MeV, about 285 MeV,about 290 MeV, about 295 MeV, or about 300 MeV or higher. The range canalso have a lower boundary that is about 100 MeV or lower to about 200MeV, e.g., about 100 MeV or lower, about 105 MeV, about 110 MeV, about115 MeV, about 120 MeV, about 125 MeV, about 130 MeV, about 135 MeV,about 140 MeV, about 145 MeV, about 150 MeV, about 155 MeV, about 160MeV, about 165 MeV, about 170 MeV, about 175 MeV, about 180 MeV, about185 MeV, about 190 MeV, about 195 MeV, about 200 MeV.

In some examples, the variation is non-continuous and the variation stepcan have a size of about 10 MeV or lower, about 15 MeV, about 20 MeV,about 25 MeV, about 30 MeV, about 35 MeV, about 40 MeV, about 45 MeV,about 50 MeV, about 55 MeV, about 60 MeV, about 65 MeV, about 70 MeV,about 75 MeV, or about 80 MeV or higher. Varying the energy by one stepsize can take no more than 30 minutes, e.g., about 25 minutes or less,about 20 minutes or less, about 15 minutes or less, about 10 minutes orless, about 5 minutes or less, about 1 minute or less, or about 30seconds or less. In other examples, the variation is continuous and theaccelerator can adjust the energy of the particle beam at a relativelyhigh rate, e.g., up to about 50 MeV per second, up to about 45 MeV persecond, up to about 40 MeV per second, up to about 35 MeV per second, upto about 30 MeV per second, up to about 25 MeV per second, up to about20 MeV per second, up to about 15 MeV per second, or up to about 10 MeVper second. The accelerator can be configured to adjust the particleenergy both continuously and non-continuously. For example, acombination of the continuous and non-continuous variation can be usedin a treatment of one target volume or in treatments of different targetvolumes. Flexible treatment planning and flexible treatment can beachieved.

A particle accelerator that outputs a particle beam having a variableenergy can provide accuracy in irradiation treatment and reduce thenumber of additional devices (other than the accelerator) used for thetreatment. For example, the use of degraders for changing the energy ofan output particle beam may be reduced or eliminated. The properties ofthe particle beam, such as intensity, focus, etc. can be controlled atthe particle accelerator and the particle beam can reach the targetvolume without substantial disturbance from the additional devices. Therelatively high variation rate of the beam energy can reduce treatmenttime and allow for efficient use of the treatment system.

In some implementations, the accelerator, such as the synchrocyclotron502 of FIG. 1, accelerates particles or particle beams to variableenergy levels by varying the magnetic field in the accelerator, whichcan be achieved by varying the electrical current applied to coils forgenerating the magnetic field. As shown in FIGS. 3, 4, 5, 6, and 7,example synchrocyclotron 10 (502 in FIG. 1) includes a magnet systemthat contains a particle source 90, a radiofrequency drive system 91,and a beam extraction system 38. FIG. 26 shows an example of a magnetsystem that may be used in a variable-energy accelerator. In thisexample implementation, the magnetic field established by the magnetsystem 1012 can vary by about 5% to about 35% of a maximum value of themagnetic field that two sets of coils 40 a and 40 b, and 42 a and 42 bare capable of generating. The magnetic field established by the magnetsystem has a shape appropriate to maintain focus of a contained protonbeam using a combination of the two sets of coils and a pair of shapedferromagnetic (e.g., low carbon steel) structures, examples of which areprovided above.

Each set of coils may be a split pair of annular coils to receiveelectrical current. In some situations, both sets of coils aresuperconducting. In other situations, only one set of the coils issuperconducting and the other set is non-superconducting or normalconducting (also discussed further below). It is also possible that bothsets of coils are non-superconducting. Suitable superconductingmaterials for use in the coils include niobium-3 tin (Nb3Sn) and/orniobium-titanium. Other normal conducting materials can include copper.Examples of the coil set constructions are described further below.

The two sets of coils can be electrically connected serially or inparallel. In some implementations, the total electrical current receivedby the two sets of coils can include about 2 million ampere turns toabout 10 million ampere turns, e.g., about 2.5 to about 7.5 millionampere turns or about 3.75 million ampere turns to about 5 millionampere turns. In some examples, one set of coils is configured toreceive a fixed (or constant) portion of the total variable electricalcurrent, while the other set of coils is configured to receive avariable portion of the total electrical current. The total electricalcurrent of the two coil sets varies with the variation of the current inone coil set. In other situations, the electrical current applied toboth sets of coils can vary. The variable total current in the two setsof coils can generate a magnetic field having a variable magnitude,which in turn varies the acceleration pathways of the particles andproduces particles having variable energies.

Generally, the magnitude of the magnetic field generated by the coil(s)is scalable to the magnitude of the total electrical current applied tothe coil(s). Based on the scalability, in some implementations, linearvariation of the magnetic field strength can be achieved by linearlychanging the total current of the coil sets. The total current can beadjusted at a relatively high rate that leads to a relatively high-rateadjustment of the magnetic field and the beam energy.

In the example reflected in Table 1 above, the ratio between values ofthe current and the magnetic field at the geometric center of the coilrings is: 1990:8.7 (approximately 228.7:1); 1920:8.4 (approximately228.6:1); 1760:7.9 (approximately 222.8:1). Accordingly, adjusting themagnitude of the total current applied to a superconducting coil(s) canproportionally (based on the ratio) adjust the magnitude of the magneticfield.

The scalability of the magnetic field to the total electrical current inthe example of Table 1 is also shown in the plot of FIG. 24, where BZ isthe magnetic field along the Z direction; and R is the radial distancemeasured from a geometric center of the coil rings along a directionperpendicular to the Z direction. The magnetic field has the highestvalue at the geometric center, and decreases as the distance Rincreases. The curves 1035, 1037 represent the magnetic field generatedby the same coil sets receiving different total electrical current: 1760Amperes and 1990 Amperes, respectively. The corresponding energies ofthe extracted particles are 211 MeV and 250 MeV, respectively. The twocurves 1035, 1037 have substantially the same shape and the differentparts of the curves 1035, 1037 are substantially parallel. As a result,either the curve 1035 or the curve 1037 can be linearly shifted tosubstantially match the other curve, indicating that the magnetic fieldis scalable to the total electrical current applied to the coil sets.

In some implementations, the scalability of the magnetic field to thetotal electrical current may not be perfect. For example, the ratiobetween the magnetic field and the current calculated based on theexample shown in table 1 is not constant. Also, as shown in FIG. 24, thelinear shift of one curve may not perfectly match the other curve. Insome implementations, the total current is applied to the coil setsunder the assumption of perfect scalability. The target magnetic field(under the assumption of perfect scalability) can be generated byadditionally altering the features, e.g., geometry, of the coils tocounteract the imperfection in the scalability. As one example,ferromagnetic (e.g., iron) rods (magnetic shims) can be inserted orremoved from one or both of the magnetic structures (e.g., pole pieces).The features of the coils can be altered at a relatively high rate sothat the rate of the magnetic field adjustment is not substantiallyaffected as compared to the situation in which the scalability isperfect and only the electrical current needs to be adjusted. In theexample of iron rods, the rods can be added or removed at the time scaleof seconds or minutes, e.g., within 5 minutes, within 1 minute, lessthan 30 seconds, or less than 1 second.

In some implementations, settings of the accelerator, such as thecurrent applied to the coil sets, can be chosen based on the substantialscalability of the magnetic field to the total electrical current in thecoil sets.

Generally, to produce the total current that varies within a desiredrange, any combination of current applied to the two coil sets can beused. In an example, the coil set 42 a, 42 b can be configured toreceive a fixed electrical current corresponding to a lower boundary ofa desired range of the magnetic field. In the example shown in table 1,the fixed electrical current is 1760 Amperes. In addition, the coil set40 a, 40 b can be configured to receive a variable electrical currenthaving an upper boundary corresponding to a difference between an upperboundary and a lower boundary of the desired range of the magneticfield. In the example shown in table 1, the coil set 40 a, 40 b isconfigured to receive electrical current that varies between 0 Ampereand 230 Amperes.

In another example, the coil set 42 a, 42 b can be configured to receivea fixed electrical current corresponding to an upper boundary of adesired range of the magnetic field. In the example shown in table 1,the fixed current is 1990 Amperes. In addition, the coil set 40 a, 40 bcan be configured to receive a variable electrical current having anupper boundary corresponding to a difference between a lower boundaryand an upper boundary of the desired range of the magnetic field. In theexample shown in table 1, the coil set 40 a, 40 b is configured toreceive electrical current that varies between −230 Ampere and 0 Ampere.

The total variable magnetic field generated by the variable totalcurrent for accelerating the particles can have a maximum magnitudegreater than 4 Tesla, e.g., greater than 5 Tesla, greater than 6 Tesla,greater than 7 Tesla, greater than 8 Tesla, greater than 9 Tesla, orgreater than 10 Tesla, and up to about 20 Tesla or higher, e.g., up toabout 18 Tesla, up to about 15 Tesla, or up to about 12 Tesla. In someimplementations, variation of the total current in the coil sets canvary the magnetic field by about 0.2 Tesla to about 4.2 Tesla or more,e.g., about 0.2 Tesla to about 1.4 Tesla or about 0.6 Tesla to about 4.2Tesla. In some situations, the amount of variation of the magnetic fieldcan be proportional to the maximum magnitude.

FIG. 25 shows an example RF structure for sweeping the voltage on thedee plate 100 over an RF frequency range for each energy level of theparticle beam, and for varying the frequency range when the particlebeam energy is varied. The semicircular surfaces 103, 105 of the deeplate 100 are connected to an inner conductor 1300 and housed in anouter conductor 1302. The high voltage is applied to the dee plate 100from a power source (not shown, e.g., an oscillating voltage input)through a power coupling device 1304 that couples the power source tothe inner conductor. In some implementations, the coupling device 1304is positioned on the inner conductor 1300 to provide power transfer fromthe power source to the dee plate 100. In addition, the dee plate 100 iscoupled to variable reactive elements 1306, 1308 to perform the RFfrequency sweep for each particle energy level, and to change the RFfrequency range for different particle energy levels.

The variable reactive element 1306 can be a rotating capacitor that hasmultiple blades 1310 rotatable by a motor (not shown). By meshing orunmeshing the blades 1310 during each cycle of RF sweeping, thecapacitance of the RF structure changes, which in turn changes theresonant frequency of the RF structure. In some implementations, duringeach quarter cycle of the motor, the blades 1310 mesh with the eachother. The capacitance of the RF structure increases and the resonantfrequency decreases. The process reverses as the blades 1310 unmesh. Asa result, the power required to generate the high voltage applied to thedee plate 103 and necessary to accelerate the beam can be reduced by alarge factor. In some implementations, the shape of the blades 1310 ismachined to form the required dependence of resonant frequency on time.

The RF frequency generation is synchronized with the blade rotation bysensing the phase of the RF voltage in the resonator, keeping thealternating voltage on the dee plates close to the resonant frequency ofthe RF cavity. (The dummy dee is grounded and is not shown in FIG. 25).

The variable reactive element 1308 can be a capacitor formed by a plate1312 and a surface 1316 of the inner conductor 1300. The plate 1312 ismovable along a direction 1314 towards or away from the surface 1316.The capacitance of the capacitor changes as the distance D between theplate 1312 and the surface 1316 changes. For each frequency range to beswept for one particle energy, the distance D is at a set value, and tochange the frequency range, the plate 1312 is moved corresponding to thechange in the energy of the output beam.

In some implementations, the inner and outer conductors 1300, 1302 areformed of a metallic material, such as copper, aluminum, or silver. Theblades 1310 and the plate 1312 can also be formed of the same ordifferent metallic materials as the conductors 1300, 1302. The couplingdevice 1304 can be an electrical conductor. The variable reactiveelements 1306, 1308 can have other forms and can couple to the dee plate100 in other ways to perform the RF frequency sweep and the frequencyrange alteration. In some implementations, a single variable reactiveelement can be configured to perform the functions of both the variablereactive elements 1306, 1308. In other implementations, more than twovariable reactive elements can be used.

Any two more of the foregoing implementations may be used in anappropriate combination in an appropriate particle accelerator (e.g., asynchrocyclotron). Likewise, individual features of any two more of theforegoing implementations may be used in an appropriate combination.

Elements of different implementations described herein may be combinedto form other implementations not specifically set forth above. Elementsmay be left out of the processes, systems, apparatus, etc., describedherein without adversely affecting their operation. Various separateelements may be combined into one or more individual elements to performthe functions described herein.

The example implementations described herein are not limited to use witha particle therapy system or to use with the example particle therapysystems described herein. Rather, the example implementations can beused in any appropriate system that directs accelerated particles to anoutput.

Additional information concerning the design of an exampleimplementation of a particle accelerator that may be used in a system asdescribed herein can be found in U.S. Provisional Application No.60/760,788, entitled “High-Field Superconducting Synchrocyclotron” andfiled Jan. 20, 2006; U.S. patent application Ser. No. 11/463,402,entitled “Magnet Structure For Particle Acceleration” and filed Aug. 9,2006; and U.S. Provisional Application No. 60/850,565, entitled“Cryogenic Vacuum Break Pneumatic Thermal Coupler” and filed Oct. 10,2006, all of which are incorporated herein by reference.

The following applications are incorporated by reference into thesubject application: the U.S. Provisional Application entitled“CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No. 61/707,466),the U.S. Provisional Application entitled “ADJUSTING ENERGY OF APARTICLE BEAM” (Application No. 61/707,515), the U.S. ProvisionalApplication entitled “ADJUSTING COIL POSITION” (Application No.61/707,548), the U.S. Provisional Application entitled “FOCUSING APARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No.61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELDREGENERATOR” (Application No. 61/707,590), the U.S. ProvisionalApplication entitled “FOCUSING A PARTICLE BEAM” (Application No.61/707,704), the U.S. Provisional Application entitled “CONTROLLINGPARTICLE THERAPY (Application No. 61/707,624), and the U.S. ProvisionalApplication entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR”(Application No. 61/707,645).

The following are also incorporated by reference into the subjectapplication: U.S. Pat. No. 7,728,311 which issued on Jun. 1, 2010, U.S.patent application Ser. No. 11/948,359 which was filed on Nov. 30, 2007,U.S. patent application Ser. No. 12/275,103 which was filed on Nov. 20,2008, U.S. patent application Ser. No. 11/948,662 which was filed onNov. 30, 2007, U.S. Provisional Application No. 60/991,454 which wasfiled on Nov. 30, 2007, U.S. Pat. No. 8,003,964 which issued on Aug. 23,2011, U.S. Pat. No. 7,208,748 which issued on Apr. 24, 2007, U.S. Pat.No. 7,402,963 which issued on Jul. 22, 2008, U.S. patent applicationSer. No. 13/148,000 filed Feb. 9, 2010, U.S. patent application Ser. No.11/937,573 filed on Nov. 9, 2007, U.S. patent application Ser. No.11/187,633, titled “A Programmable Radio Frequency Waveform Generatorfor a Synchrocyclotron,” filed Jul. 21, 2005, U.S. ProvisionalApplication No. 60/590,089, filed on Jul. 21, 2004, U.S. patentapplication Ser. No. 10/949,734, titled “A Programmable ParticleScatterer for Radiation Therapy Beam Formation”, filed Sep. 24, 2004,and U.S. Provisional Application No. 60/590,088, filed Jul. 21, 2005.

Any features of the subject application may be combined with one or moreappropriate features of the following: the U.S. Provisional Applicationentitled “CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No.61/707,466), the U.S. Provisional Application entitled “ADJUSTING ENERGYOF A PARTICLE BEAM” (Application No. 61/707,515), the U.S. ProvisionalApplication entitled “ADJUSTING COIL POSITION” (Application No.61/707,548), the U.S. Provisional Application entitled “FOCUSING APARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No.61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELDREGENERATOR” (Application No. 61/707,590), the U.S. ProvisionalApplication entitled “FOCUSING A PARTICLE BEAM” (Application No.61/707,704), the U.S. Provisional Application entitled “CONTROLLINGPARTICLE THERAPY (Application No. 61/707,624), and the U.S. ProvisionalApplication entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR”(Application No. 61/707,645), U.S. Pat. No. 7,728,311 which issued onJun. 1, 2010, U.S. patent application Ser. No. 11/948,359 which wasfiled on Nov. 30, 2007, U.S. patent application Ser. No. 12/275,103which was filed on Nov. 20, 2008, U.S. patent application Ser. No.11/948,662 which was filed on Nov. 30, 2007, U.S. ProvisionalApplication No. 60/991,454 which was filed on Nov. 30, 2007, U.S. patentapplication Ser. No. 13/907,601, which was filed on May 31, 2013, U.S.patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, U.S.Pat. No. 8,003,964 which issued on Aug. 23, 2011, U.S. Pat. No.7,208,748 which issued on Apr. 24, 2007, U.S. Pat. No. 7,402,963 whichissued on Jul. 22, 2008, U.S. patent application Ser. No. 13/148,000filed Feb. 9, 2010, U.S. patent application Ser. No. 11/937,573 filed onNov. 9, 2007, U.S. patent application Ser. No. 11/187,633, titled “AProgrammable Radio Frequency Waveform Generator for a Synchrocyclotron,”filed Jul. 21, 2005, U.S. Provisional Application No. 60/590,089, filedon Jul. 21, 2004, U.S. patent application Ser. No. 10/949,734, titled “AProgrammable Particle Scatterer for Radiation Therapy Beam Formation”,filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088,filed Jul. 21, 2005.

Except for the provisional application from which this patentapplication claims priority and the documents incorporated by referenceabove, no other documents are incorporated by reference into this patentapplication.

Other implementations not specifically described herein are also withinthe scope of the following claims.

What is claimed is:
 1. A particle accelerator comprising: a voltagesource to provide a radio frequency (RF) voltage to a cavity toaccelerate particles within the cavity, the cavity having a magneticfield causing the particles to move orbitally within the cavity; anextraction channel to receive the particles from the cavity and tooutput the received particles from the cavity; and a regenerator toprovide a magnetic field change within the cavity to thereby changeorbits of particles within the cavity so that, eventually, the particlesoutput to the extraction channel, the regenerator comprising an edgecomprising a non-orthogonal intersection of two faces; wherein themagnetic field in a center of the cavity is at least 6 Tesla.
 2. Theparticle accelerator of claim 1, wherein the regenerator comprises aferromagnetic arrangement located at a radial location from a center ofthe cavity.
 3. The particle accelerator of claim 2, wherein theregenerator comprises a single ferromagnetic arrangement.
 4. Theparticle accelerator of claim 1, wherein the regenerator includes steel.5. The particle accelerator of claim 1, wherein the magnetic field is atmost 20 Tesla and the magnetic field change comprises a magnetic fieldbump that is at most 2 Tesla.
 6. The particle accelerator of claim 1,wherein the magnetic field change comprises a magnetic field bump; andwherein the regenerator is designed to produce the magnetic field bumpIQ have a specific shape and/or magnitude that is based on a number ofthe particles to enter the extraction channel.
 7. The particleaccelerator of claim 1, wherein the edge comprises a single edge thatfaces toward a center of the cavity.
 8. The particle accelerator ofclaim 1, wherein the extraction channel comprises a septum thatseparates the particles entering the extraction channel from otherparticles, the regenerator being configured so that a pitch and an angleof a particle orbit enable a majority of particles in the particle orbitto pass over the septum and into the extraction channel.
 9. The particleaccelerator of claim 8, wherein the particles passing over the septumare within a range of orbits of particles relative to a center of thecavity.
 10. A proton therapy system comprising: the particle acceleratorof claim 1; and a gantry on which the particle accelerator is mounted,the gantry being rotatable relative to a patient position; wherein theparticles comprise protons that are output essentially directly from theparticle accelerator to the patient position.
 11. The proton therapysystem of claim 10, wherein the particle accelerator comprises asynchrocyclotron.
 12. The particle accelerator of claim 11, wherein theparticles received by the extraction channel from the cavity compriseless than all particles in the orbit.
 13. The particle accelerator ofclaim 1, wherein the two faces are not parallel to, or perpendicular to,a mid-plane of the particle accelerator.
 14. The particle accelerator ofclaim 13, wherein the regenerator is movable within the cavity.
 15. Theparticle accelerator of claim 14, wherein the regenerator is movabletowards or away from a center of the cavity.
 16. The particleaccelerator of claim 11, wherein the particles output to the extractionchannel comprise less than all particles in an orbit.
 17. A particleaccelerator comprising: a particle source to provide particles to acavity; a voltage source to provide a radio frequency (RF) voltage tothe cavity to accelerate the particles within the cavity, the particlesaccelerated within the cavity traveling in an orbit within the cavity;an extraction channel to receive the particles from the cavity foroutput from the particle accelerator; and a regenerator to provide amagnetic field bump within the cavity to change the orbit of theparticles in order to direct the particles in the orbit toward theextraction channel, the regenerator comprising intersecting faces thatare not parallel to, or perpendicular to, a mid-plane of the particleaccelerator.
 18. The particle accelerator of claim 17, wherein amagnetic field in a center of the cavity is at least 4 Tesla.
 19. Theparticle accelerator of claim 17, wherein the magnetic field bump is atmost 2 Tesla.
 20. The particle accelerator of claim 17, wherein theregenerator is movable in one or more dimensions relative to a center ofthe cavity.
 21. The particle accelerator of claim 17, wherein theregenerator is designed to produce the magnetic field bump to have aspecific shape and/or magnitude that is based on a number of theparticles to enter the extraction channel.
 22. The particle acceleratorof claim 21, wherein a magnetic field in a center of the cavity is atleast 6 Tesla.
 23. The particle accelerator of claim 17, wherein theextraction channel comprises a septum that separates the particlesentering the extraction channel from other particles, the regeneratorbeing configured so that a pitch and an angle of the orbit enable amajority of the particles in the orbit to pass over the septum and intothe extraction channel.
 24. The particle accelerator of claim 17,wherein particles that pass over the septum are within a range of orbitsof particles relative to a center of the cavity.
 25. A proton therapysystem comprising: the particle accelerator of claim 17; and a gantry onwhich the particle accelerator is mounted, the gantry being rotatablerelative to a patient position; wherein the particles comprise protonsthat are output essentially directly from the particle accelerator tothe patient position.
 26. The proton therapy system of claim 25, whereinthe particle accelerator comprises a synchrocyclotron.
 27. A particleaccelerator comprising: a voltage source to provide a radio frequency(RF) voltage to a cavity to accelerate particles within the cavity, thecavity having a magnetic field causing the particles accelerated to moveorbitally within the cavity; an extraction channel to receive at leastsome of the particles accelerated and to output the at least some of theparticles from the cavity; and a regenerator to change a magnetic fieldwithin the cavity to thereby change successive orbits of the particlesaccelerated so that, eventually, the at least some of the particlesoutput to the extraction channel, the regenerator comprising an edgeformed by a non-orthogonal intersection of two faces, where the twofaces are not parallel to, or perpendicular to, a mid-plane of theparticle accelerator.
 28. The particle accelerator of claim 18, whereinthe regenerator is movable within the cavity.
 29. The particleaccelerator of claim 28, wherein the regenerator is movable towards oraway from a center of the cavity.
 30. The particle accelerator of claim18, wherein the faces intersect at an edge that faces an interior of thecavity.
 31. The particle accelerator of claim 27, wherein the particleaccelerator is configured to vary an energy of the particles that moveorbitally within the cavity; and wherein the regenerator is movable inone or more dimensions within the cavity, where movement of theregenerator is based on an energy of the particles.
 32. The particleaccelerator of claim 11, further comprising: coils to pass current togenerate the magnetic field, wherein a variation in an amount of currentthrough the coils corresponds to a variation in an energy of theparticles.
 33. The particle accelerator of claim 31, further comprising:an energy degrader to affect an energy of a particle beam output fromthe particle accelerator.